In some wellbore operations and/or systems, it may be helpful to confirm or correlate a particular depth within the wellbore, such as, for example, to confirm a treatment depth for a particular operation. Depth may be correlated using known reference points on a tubular, such as a casing string. Electric logging tools may detect a magnetic anomaly caused by the relatively high mass of a casing collar on a tubular string, as compared to the tubular joints. A signal may be transmitted to surface equipment that provides an output to be correlated with previous logs and known casing features.